elisp quicksort

quicksort.el

;; https://harryrschwartz.com/2014/04/08/an-introduction-to-emacs-lisp.html
;; this is amazing
(require 'cl-remove-if-not)

(defun quicksort (items)
  (if (null items)
      nil
    (let* ((pivot (car items))
	        (rest (cdr items))
	        (lesser (cl-remove-if-not (lambda (x) (<= x pivot)) rest))
	        (greater (cl-remove-if-not (lambda (x) (> x pivot)) rest)))
     (append (quicksort lesser) (list pivot) (quicksort greater)))))

(quicksort `(5 8 3 0 4 7 2 1 4 3 5 9))